SODIUM SALTS . 145 



nitrification in soils, Renault claims that slow ammonification and 

 subsequent nitrification is always accompanied by a low percentage 

 of potash. Dumont's experiments showed that potassium car- 

 bonate, added to a soil at the rate of from 1 to 2.5 gm. per 1000 gm. 

 of soil, markedly increased nitrification, but that larger applications 

 of the salt progressively diminished the rate of nitrification, while 

 the addition of 8 gm. to 1000 gm. of soil completely checked it. 

 Lumia concluded that potassium chlorid and sulphate were nearly 

 as effective in promoting the activity of alcoholic ferments as were 

 phosphates. 



Fred and Hart found that both calcium and potassium sulphates 

 increased ammonification in solution and that the sulphates of potas- 

 sium, calcium, and magnesium each increased the volume of carbon 

 dioxid from soil. From the results obtained with different salts, 

 they conclude that the addition of the potassium ion did not mate- 

 rially increase ammonification in the soil examined. 



Sodium Salts. Sodium salts are often used as fertilizers and with 

 good results. Furthermore, many alkali soils contain sodium salts 

 in quantities sufficient to be toxic to both the higher and lower 

 plants. For these reasons many investigations have been conducted 

 to determine the influence of sodium compounds upon higher 

 plants, and many have had as their object the determination of their 

 influence upon soil bacteria. 



As early as 1884 Warington showed that the presence of 0.032 

 per cent, of sodium bicarbonate distinctly retarded nitrification, 

 and that in the presence of 0.096 per cent, nitrification was very 

 slight. Schlosing had added various salts to the soil in quantities 

 not exceeding 485 parts per million with no apparent effect upon 

 nitrification. However, Deherain found that common salt com- 

 menced to be harmful when it exceeded one-thousandth of the weight 

 of soil, and when larger quantities -are applied nitrification almost 

 ceased. According to the same observer sodium nitrate may stop 

 nitrification for a time, but later it recommences. Lipman and 

 others found that sodium nitrate increased the accumulation of 

 nitrates in a soil. They found, however, a certain periodicity in 

 the accumulation of nitrates which would account for the different 

 results reported by various investigators. In later investigators they 

 concluded that at times sodium nitrate stimulates ammonification. 

 McBeth and Wright found that carbonates, chlorids, and sulphates 

 inhibited nitrification and that the former were more injurious than 

 the latter. 



The most far-reaching and systematic work which has been 

 reported on the influence of salts upon bacterial activity is the 

 excellent work by C. B. Lipman who demonstrated that ammonifi- 

 cation is inhibited by sodium chlorid, sodium sulphate, and sodium 

 carbonate. The points at which the salts became toxic are: for 

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